Secondary electron discharge device



y 1939- A. J. w. M. VAN OVERBEEK El AL 2,167,097

SECONDARY ELECTRON DISCHARGE DEVICE Filed Aug. 25, 1957 l E OUTPUT |||||||}--1||||||,

INPUT HHIIII INVENTORS ADR/ANg/S J. WM. VAN OVEREEEK BY I AND EDMUND H. MPP

- ATTORNEY.

Patented July 25, 1939 UNITED STATES SECONDARY ELEo'moN DISCHARGE DEVICE 'Adrianus J. W. M. van Overbeek and Edmund H. Liipp, Eindhoven, Netherlands, assignors to N. V. Philips Gloeilampeni'abrieken, Eindhoven,

Netherlands Application August 25, 1937, Serial No.-160,796

In the Netherlands September 1, 1936 3 Claims.

This invention relates to an electron discharge tube having an electrode system including a secondary electron emission electrode or emitter with a surface having such properties that on being struck by a primary electron a plurality of secondary electrons emerge from it, so that the ratio of the number of secondary electrons to the number of primary electrons is greater than unity.

Tubes of the type referred to have been used with satisfactory results, but i'n'certain cases difficulties arise because an increase in anode voltage causes an excessive increase in anode current, resulting, for example, in a reduction of the interal resistance, which may be objectionable in the operation of the tube. l

' 'I'heprincipal object of the invention is to provide an improved tube of the type referred to in l which diificulties due to excessive increase of output current with increase of anode voltage are'avoided.

It has been found that in an electric-discharge tube with an electrode system which includes a secondary emission electrode such difllculties' can be minimized and practically eliminated by the use, according to the present invention, of means for causing-the number of primary electrons \impinging on a layer mounted 'on "a secondary emission electrode to decrease as the anode voltage increases. As a result the current which passes-fromthe secondary emission electrode to the anode decreases and the internal resistance may increase or even become negative.

In one particularembodiment of the present invention a discharge tube, with an electrode system so constructed that electrons emerging from the cathode are united to form one or more beams, has the anode out of the path of the primary electron beam and the secondary emission electrode is coated on only part of its'surface with a substance which is capable of emitting secondary electrons. the tube become wider or narrower as the anode voltage increases or decreases, so that the part of the secondary emission electrode which 'is coated with a substance readily emitting secondary electrons is struck to agreater or less extent by the primary electrons. I

the anode is in the path of and can be' struck as the anode voltage increases or decreases, a

greater or less number of primary electrons find Thus, the electron beams in their way to the anode by reason of the electron beam becoming wider or narrower.

In addition it has been found that a mean constant density and a constant internal resistance can be obtained if the edge of .the secondary emission electrode is not entirely parallel to the edge of the electron beam or is not symmetrical to this beam. To this end, the edge of the secondary emission electrode may, for example, be notched; the edge of the electron emitting layer on this electrode may be indented; or the electrode 'may be arranged asymmetrically in the tube; the effect of which 'may also be obtained by making the beam or beams asymmetrical t0 the remainder of the tube, for example, by using beam forming electrodes of a suitable construction. f

In order that the invention may be more clearly understood and readily carried into eifect it will now be described more fully with referenceto,

the accompanying drawing, in which Figures 1 and 2 show diagrammatically and in cross section two forms of electrode systems for an electric discharge tube according to the invention, and Figures 3 and 4 are plan views to showsuitable, shapes for the secondary emission electrode..'

The tube shown in Figure 1 comprises a rectilinear cathode I, such as an indirectly heated cathode, and a control electrodeformed by four" straight rods 2 parallelto the cathode and equally spaced about the cathode. These rods are connected to constitute an equipotential grid. A second or accelerating electrode of fourtroughlike slats 3 equally spaced about the cathode and each in radial'alignment with arod ofthe control grid, surrounds the control grid, with the spaces between the slats 3 in alignment with the spaces between the grid rods 2. "This electrode struc ture concentrates the discharge from the cathode into four radial beams which emerge from, the spaces between the slats 3. An output anode of four strips '4, each in radial alignment with a control gridrod 2 and with an accelerating ielectrode slat 3, and of'such width thatits edges are in radial'alignment with the edges ofthe corre; sponding slat 3, surrounds the accelerating electrode. The spaces between the'edges of the strips I' I 4 are apertures in the output anode. second In another embodiment of the invention the electrode system is so arranged in the tube that.

anode element or secondary electron emitter 5, preferably an imperforate cylinder surrounding the output anode, is mounted to intercept the" electron beams" which emerge radially from thej accelerating electrode andpass through the spaces between the edges of the anode strips 4; The radial electron beams impinge on the emitter 5 and cause the emission of secondary electrons, which go to the anode. With variations in anode potential the beams become wider and narrower, and as a result more or less of the primary electrons in the beams reach the anode directly. If, for example, the anode voltage is such that the beam emerging from the accelerating electrode is narrow, few primary electrons reach the anode, and practically all of them reach the secondary electron emitter l; as the anode voltage increases, the beam widens, whereupon more of the primary electrons in the beam reach the anode directly, and less of them reach the secondary electron emitter I. The ratio of primary electrons to secondary electrons reaching the anode depends on the width of the beams, which in turn is de-' pendent on the anode voltage.

In Figure 2 is shown a modification having a control grid I: of the conventional wound grid type, a duplex accelerating electrode l3 comprising two parallel metal sheets mounted on opposite sides of the control grid and connected together, and an anode comprising four parallel flat members ll arranged in two pairs, each pair mounted beyond the ends of the accelerating electrode II and spaced at a distance at least as great as the spacing between the accelerating electrode sheets ii. The accelerating electrode forms the discharge from the cathode into two diametrically opposite beams which emerge from opposite ends of the accelerating electrode. Each beam passes through the space between the corresponding pair of anode members. The beams which pass the anode are intercepted by a duplex secondary emission electrode ll comprising two metal sheets extending across the paths of the beams, each sheet being in register with and wider than the space between the corresponding output anode members, and having on the surface facing the cathode a secondary electron emitter strip I! in register with and narrower than that space and preferably of material having good secondary electron emissivity, such as a coating of alkaline earth metal oxides. As only the middle portion of the surface of the metal sheet is coated, there is left along each edge of the strip ll a band of uncoated metal which has very poor secondary electron emissivity. Since the secondary emission electrode II is opposite only that part of the electrode system from which the beams emerge. and is coated over only a part II of its surface with a substance that readily emits a secondary electrons, the beam on widening and narrowing strikes more or less that part of the secondary emission electrode outside the edges of the part It which is not coated with the substance that readily emits secondary electrons.

In Figures 1 and 2 the path of the discharge to the secondary electron emission electrode and thence to the anode is indicated by lines with light arrows, and of the discharge directly to the anode or to the uncoated part ofthe secondary electron emission electrode II by heavy arrows marked with two arrow heads. The discharge, emerging from the accelerating electrode as a beam, passes through an aperture in the output anode and impinges on the second anode element or secondary electron emitter. The width of the beam changes with changes in anode potential. The size of aperture in the anode is so chosen that the proportion of the discharge which reaches the anode directly is dependent on the beam width, and the secondary electron emitter is so made or so shaped that the amount of secondary emission is also dependent on beam width,

Figures 3 and 4 show modifications in the shape of the secondary electron emitter II. In its form shown in Figure 3 such an electrode or emitter, which may be of various shapes and sizes, comprises a metal sheet with the edge which corresponds to a straight side of the aperture in the output anode made irregular, for example by notches or indentations II in the edge. When the electron beam overlaps this irregular edge the secondary electron emission is less than in the case where the edge is straight. In Figure 4 the secondary electron emitter is a fiat sheet wider at the upper than at the lower end, so that for a part of its length the electrode is narrower than the aperture in the output anode. In this figure the broken lines ll indicate a position of the electron beam in which the electrode intercepts all of the beam falling on the upper or wide part and only part of the beam falling on the lower or narrow part. In both Figures 3 and 4 the secondary emitter is asymmetrical to said cathode than said output anode and comprising a metal sheet wider than the aperture in said output anode, said anode element having on the surface facing said aperture a coated portion of high secondary electron emissivity in register with said aperture and narrower than said metal sheet.

2. An electron discharge tube comprising an electrode system including a cathode, an output anode having an aperture, a beam forming electrode between said cathode and said output anode for concentrating the discharge from said cathode to said output anode into an electron beam directed through said aperture in said anode, and a second anode element further from said cathode than said output anode and extending transversely of the axis of the electron beam, said second anode element being wider than said aperture and having opposite said aperture a sur- 1 face of high secondary electron emissivity which is narrower than said aperture in said output anode and is within the projection of said aperture on the planeof said second anode element.

3. An electron discharge tube comprising an electrode system including a cathode, an output anode having an aperture with a straight side, a beam forming electrode between said cathode and said output anode for concentrating the discharge from said cathode to said output a anode into an electron beam directed through said aperture in said output anode, and a second anode element further from said cathode than said output anode with a surface of high secondary electron emissivity exposed through the aperture in said output anode to the cathode and having an irregular edge corresponding to. the straight side of said aperture and within the projection of said aperture on the plane of said second anode element.

ADRIANUS J. w. M. VAN ovnmanax. EDMUND H. LOPP. 

